The present invention relates to a surveillance control apparatus for a security system such as a fire alarm system, a smoke damper system, a gas leakage alarm system, a burglar alarm system and so on, which monitors and controls a plurality of terminal devices in a concentrated manner under the control of a central station.
In a conventional surveillance control apparatus of the type wherein a plurality of terminal devices such as a smoke detector, a temperature sensor, a photosensor, a gas detector, a fire partition and a smoke damper are connected in parallel to each other on a line extending from a central station, inherent addresses are assigned by the central station to the respective terminal devices. When a self address detector of a given terminal device detects an address signal representing the inherent address thereof and generating from the central station, the terminal device sends back a detection signal to the central station. Each terminal device also receives a control signal from the central station. This conventional system is generally called a polling system which decreases the number of lines between the central station and the terminal devices. However, since all the terminal devices are usually accessed by the central station, in a system such as a fire alarm system which requires high reliability, the entire system power must be cut off in order to prevent operation of control terminal devices such as smoke dampers or local bell units, and must be deenergized to prevent an erroneous alarm when the failure of any terminal device occurs. However, deenergization of the entire system and the local bell units results in the entire half of all system functions. Even if a fire alarm system is being installed in a construction site of a building or the like, the system cannot be operated unless the building is completely constructed. As a result, the conventional fire alarm system of this type cannot satisfy the on-the-spot needs.
In Japanese Patent Application No. 58-223142 filed Nov. 29, 1983, entitled "Surveillance Control Apparatus for Security System", incorporated herein by reference, the central station registers an address of a given terminal device and determines whether or not the given terminal device is accessed in accordance with a signal entered at a key input section. The central station refers to a registration state before each terminal device is accessed and determines whether or not this terminal device is accessed, thus solving the above-mentioned conventional problem. When a failure occurs in a terminal device, the central station registers the address of the failed terminal device, and the terminal device is not accessed. Before the respective terminal devices are accessed, the central station refers to the registration state and will not access the terminal device whose access is inhibited. The central station then accesses the next terminal device skipping the inhibited terminal device. As a result, without interrupting the operation of the system as a whole, the detection operation can be performed.
According to the apparatus proposed by the Japanese Patent Application No. 58-223142, filed Nov. 29, 1983, the breakdown state of the entire system can be prevented, and the central station can check an inhibited terminal device. However, the terminal device cannot detect whether or not it is accessed. In other words, maintenance personnel cannot know whether or not the terminal device is operated within the system, thus presenting a new problem when the reliability of the surveillance control apparatus is to be improved.
When the surveillance control apparatus is used in a gas leakage alarm system, a new problem is also presented. In a rental apartment house, gas leakage detectors operated by a commercial power source are installed in the respective apartments, and detection signals from the sensors are monitored in a concentrated monitor room. In a rental apartment house of this type, when a vacant apartment becomes available, the corresponding gas leakage detector is deenergized, and extra power consumption is prevented. However, when the power source is cut off, a new resident who moves in this apartment may often forget to turn on the power switch.
Each terminal device generates the inherent address and specific data representing whether or not the device is a fire sensor or an intrusion sensor. In addition, the terminal device converts an analog signal to a digital signal which is supplied to the central station, and also receives a control signal supplied from the central station. The terminal device having these functions comprises components most of which are formed in an integrated circuit. However, the component for setting the specific data must be a switch since data selection and updating are required. The number of contacts of the switch is increased in proportion to the number of specific data. The number of electrical parts is then increased, and the terminal device itself becomes large in size. In addition to this disadvantage, incomplete contact and accidental switching by a child or the like degrade the reliability.